The present invention is with respect to a flange connection for rectangular air-conditioning ducting having eight metal sheet frame arms in the form of open-edge box girder, which may be slipped onto the edges of one piece of rectangular ducting, and with metal anglepieces, some millimeters in thickness and each having two legs joined together by a middle plate, the legs being designed to be slipped into pieces of a box girder next to the anglepiece, the middle plate having an outer thicker corner part for spacing and generally placed on a line halving the angle between the legs of the anglepiece, the anglepieces and the box girders being joined together by fixing parts which may, for examples, be bolts.
A flange connection on these lines are to be seen in German Pat. No. 2,258,680 or in the parallel U.S. Pat. No. 3,923,326. Such designs have come into wide use in the trade.
However, for large-size air-conditioning ducting or ducting run with a high inside pressure, there is a general need for pressing together the frame arms (box girder) of two lengths of ducting with a greater force, because of this decreasing the losses caused by leaks. Furthermore, the ducting is frequently hangingly supported using specially designed structures. Such ducting is sometimes very heavy and frequently so large in size that a complete assembly team may go along inside it using special-purpose vehicles. In this respect, the forces produced by the effect of gravity have to be taken up by the legs of the anglepieces or elbows which are at right angles to each other. For reasons of rationalization and because such a connection gives a strong join, the lengths of box girders are spot-welded to the legs of the anglepieces. Frequently, however, holes may be produced in the legs of the anglepieces, into which the outer wall of a frame arm is embossed or dented, see FIGS. 1 and 2 of U.S. Pat. No. 3,923,326, such connections being acted upon by strong forces.